Filament for incandescent lamps



April 7, 1931. T, E, FOULKE 1,800,012

FILAMENT FOR INCANDESCENT LAMPS Filed Aug. 7, 1922 Hrs l Tranzsrrx Patented Apr. 7, 1931 UNITED STATES PATENT OFFICE TED E. FOULKE. F CLEVELAND, OHIO, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK FILAMENT FOR INCANDESCENT LAMPS Application led August 7, 1922. Serial N o. 579,978.

My invention relates to electric incandescent lamps and more particularly to such lamps for use where comparatively high light intensities are required. My invention is of especial advantage fon'ipicture projection apparatus, search lights, automobile head lamps, and other types of projection lamp. These lamps, as a class, are usually low voltage and high current lamps. The

1o usual practice has been to utilize coiled metallic filaments for such lamps. In the case of picture projection lamps and in other cases, it has been necessary to provide a flexible mounting so as to allow for distortion or twisting of the filament at the extremely high temperatures encountered, and at the same time, to keep the filament as much as possible in the proper position for effective results. The objects of my invention are to provide a more effective filament, and to dispense with the necessity of complicated filament mountin s.

Iccording to my invention Iutilize a filament of reflective material such as tungsten,

having its surface made up of a number of protu'berances which are so disposed and have such angles that there is sufficient inter-re? fiection to produce a substantial black body effect. Preferably, according to my invention, a ribbon filament is employed and this is so mounted as to give the maximum light radiation in the effective direction, which in the case of the picture projection is in the direction of the screen, in the case of the automobile lamp in a forward and downward direction, and so on. Ribbon filaments have been proposed heretofore for incandescent electric lamps and in some cases such filaments have been crimped. However, the crimping or corrugating of such filaments has only been slight and apparently merely for the purpose of increasing the length of the filament and allowing certain fiexibility. According to my invention, the crimping is at such angles as to obtain a substantial socalled black body effect. As explained in the Astrophysical Journal of March, 1911, pages 91 to 97 inclusive, the black body is a total radiator and has the maximum possible emissive power at any temperature. This effect may be obtained by means of a wedge of the proper angle on account of the back and forth reflection between the walls thereof. The .result has been that I have been able to obtain a very high effective brightness as compared with the coiled filaments which have been largely used, andas compared with any other filaments which have been proposed.

The disposition of the filament and of the crimps therein should be such as to obtain the maximum light in an effective direction. The angle of the crimp, that is, the angle between adjacent sections, may vary, but I have found that the maximum effective brightness is obtained where such angle is between 200 and 30o. Good results may be obtained where such angle is lower or higher than this, especially where there is a sharp line of demarcation between adjacent sections or sharp angle formed thereby as distinguished from a rounded angle. The difference of a degree is greater in effect as we get below the 20. Above 30, the falling off in effectiveness is more gradual. The so-called black body ef fect is due to the multiple reflection between the adjacent surfaces of the crimps or corrugations. The result is that the interior surfaces are more highly luminous than the areas between such crimps. In practice, the nature of the filament materia-l is such that the boundaries between crimps cannot be made mathematically straight lines but rather slightly rounded surfaces. Moreover this is necessitated in order to avoid undue weakening of these portions of the filament. The figures given above refer to tungsten laments produced according to the method disclosed in Coolidge Patent No. 1,082,933, De-

cember 30, 1913, and Paez Patent No. 1,- ,i

410,499, March 21, 1922.

In the drawing Fig. 1 is an elevation of a lamp embodying my invention; Fig. 2 is a fragmentary elevation of a modification; Fig. 3 is a horizontal section showing the fila ment diagrammatically; Fig. 4 is an elevation of a crimping device and Fig. 5 is a diagrammatic view of the filament before mounting.

The lamps illustrated in the drawing are of the type used for picture projection. That shown in Fig. 1 comprises the bulb l0 to which is sealed the stem 1l which carries embedded therein the leading-in conductors 12. The said conductors are united to the conducting filament su )ports 13 and 14 which are usually of nickel. he lamp filament in Fig. 1 comprises two strips 15 which are of tungsten ribbon, crimped in such manner as to secure the so-called black body7 effect. An auxiliary conducting support 16, united, as by welding, tothe leads of the filament strips, is carried by an insulating support 17 having supports 18, preferably of metal united, as by welding, to the conductors 13 and 14.

In the modification shown in Figs. 2 and 3, the filament 15 comprises a single strip of tungsten ribbon crimped as above described and united. as by welding, to the conducting supports 13 and 14.

The filament strips are produced by crimping tungsten ribbon lament. This may be done by means of the hand apparatus shown in Fig. 4 which comprises a lower die 19 and an upper die 20 which is reeiprocatable by cent lamps composed of material having comparatively high reflectivity and having the major portion thereof crimped so that the crimp sections make an angle with each other between 20 and 30.

4. A ribbon filament for electric incandescent lamps composed of tungsten and having the major portion thereof crimped so that the crimp sections make an angle with each other of substantially 30.

5. An electric incandescent lamp for projection purposes comprising conducting supports and a crimped ribbon filament connected to and disposed in substantially the same plane as said supports, said filament being composed of material having comparatively high reflectivity and the angle of the crimp being sharp and such that a substantial black body effect is secured.

In witness whereof, I have hereunto set my hand this 2d day of August, 1922.

TED E. FOULKE.

means of the handle 21 having a retracting spring 22. A piece of ribbon is laid upon the lower die and the upper die forced down upon it to form a V. By turning the ribbon over each time between impacts of the die the desired number of crimps may be formed. It is desirable to heat the dies, for instance, by means of the gas burner 23.

In Fig. 5, the preferred construction of the filament is shown diagrammatically. The angle between the adjacent sections., for example, angle A, is between 20 and 30.

For lamps of the type illustrated in the drawingwhich average about 400 to 2000 watt-s, with voltage from 10 to 20 volts, the filament should be from .4 cms. wide and .8 cms. long to 1 cm. wide and 1.4 cm. long. The depth of crimp should preferablyvnot eX- ceed .5 cm. to avoid distortion of filament and excessive loss of energy. The depth should preferably not be less than .3 cm. to obtain maximum effective brightness since it is desirable to reduce the area taken up by crimp ends to a minimum.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. An electric incandescent lamp filament consisting of a crimped ribbon of material having comparatively high reflectivity, the angle between adjacent sections of which is sharp and such that a substantial black body effect may be secured when such lamp is in use.

2. A ribbon filament for electric incandescent lamps composed of material having comparatively high reflectivity and having the major portion thereof crimped so that the crimp sections make an angle with each other greater than 15 and less than 45.

3. A ribbon filament for electric incandes- 

